Seismic Retrofit Method Research Articles

A case study comparing seismic retrofitting techniques for a historically significant masonry building’s minaret

Historical masonry structures are extremely susceptible to earthquakes due to their characteristic features. Seismic performance and corresponding damage patterns vary between these buildings. Even though the main structure was undamaged, many minarets suffered damage or collapsed due to the transmission of large forces from the main mass to the minaret and the abrupt changes in cross-section due to the geometry of the minaret. This study uses an ancient masonry mosque as a case study, whose minaret and main building are constructed as a single structure. The mosque’s minaret under seismic excitation is the focus of this study. The adopted model is called Alaeddin Bey Mosque in Muş, Türkiye. The seismic performance assessment of the minaret, considering various retrofitting options, is mainly based on four critical parameters: base shear, acceleration, displacement, and maximum tensile forces in all three dimensions. The analyzed retrofitting methods include base isolation located in the basement of the mosque, viscous dampers placed only in the upper part of the minaret, Carbon Fiber-Reinforced Polymer fabric fitted to only the minaret, and steel plates applied to only the minaret. Representative structural models of the mosque have been modelled with SAP2000 software. The main novelty of this study is the use of viscous dampers in the minaret. It is the first time a design methodology has been introduced for viscous damper applications in minarets. This methodology aims to prevent local damage to the minaret due to the forces generated by the dampers, while also considering the constraints of limited internal space within the minaret. The finding of this study shows that viscous damper application yields significantly better results compared to the application of Carbon Fiber-Reinforced Polymer fabric and steel plates. However, although base isolation reduces the tensile stress values throughout the entire mosque to levels well below the material’s strength, viscous damper application in the minaret significantly reduces tensile stresses only in the minaret. As a result, viscous dampers are recommended for damage reduction in the minaret only. Otherwise, base isolation should be considered for reducing stress values throughout the entire mosque including the minaret. This study contributes towards the development of new seismic retrofitting methods for historic masonry buildings ‘minaret.

Lateral load response and collapse probability of reinforced concrete shear walls retrofitted for repairability

AbstractThis paper demonstrates the efficacy of a new reinforced concrete shear wall seismic retrofit method through a series of nonlinear static and incremental dynamic analyses. Unlike traditional retrofit methods, the method investigated aims to convert conventional walls into self‐centering walls whose behavior is governed by rocking and flexure. The retrofit involves creating a cold joint at the foundation–wall interface, cutting some reinforcing bars to allow rocking, adding external post‐tensioning to enable self‐centering, and externally confining wall toes to prevent concrete crushing. The retrofit was applied to two building archetypes, each with two different shear wall designs. The four walls were retrofitted by varying retrofit parameters (portion of the vertical reinforcement bars cut, and external post‐tensioning amount). Nonlinear static and nonlinear response history analyses were performed using experimentally validated, computationally efficient models that simulate walls with fiber‐based beam–column elements. Incremental dynamic analysis was used to create collapse fragility functions for pre‐ and post‐retrofit walls. The results show that the retrofit is effective when some vertical reinforcement bars are left uncut across the foundation–wall interface. The retrofit is more effective for walls with vertical reinforcement distributed across cross‐section as compared to walls with reinforcement concentrated near boundary elements and for walls with structurally efficient amounts of reinforcement as compared to walls with higher amounts of reinforcement. This is attributed to the larger amount of reinforcement bars cut in walls with concentrated reinforcement layouts or heavy reinforcement amounts, leading to a larger loss of strength, recovery of which requires larger amounts of post‐tensioning.

Seismic Retrofitting of Existing Reinforced Concrete Buildings Using Aluminium Shear Links and Eccentric Steel Chevron Braces

Many existing reinforced concrete buildings have been designed based on earlier codes of practice that underestimated seismic forces, making them vulnerable to damage during seismic action. Equipping existing buildings with shear links and eccentric braces is one of the available seismic retrofitting methods to dissipate seismic energy away from the main structural members. In this paper, a proposal for the seismic retrofitting of two existing reinforced concrete buildings using aluminium shear links and steel braces is presented. First, a capacity-based design approach is followed to determine the required sizes of the shear links and eccentric braces. Second, numerical analyses are used to compare how the original and retrofitted buildings responded. These tests include pushover analysis, nonlinear time-history analysis, damage analysis, incremental dynamic analysis, fragility and reliability analysis, and damage analysis. The results reveal that the proposed retrofitting method can sufficiently upgrade the performance level of the buildings and reduce their storey displacements and interstorey drifts, as shear links are found to absorb almost all seismic energy, therefore keeping other structural members responding elastically. Yet, using shear links alters the local behaviour of the surrounding structural members, which should be considered in the design process. Furthermore, compared to the original buildings, retrofitted buildings are expected to undergo less structural damage as they have lower damage indices. Meanwhile, the fragility of retrofitted buildings is significantly reduced compared to the original ones, which indicates the efficiency of the proposed retrofitting methods in upgrading the performance of seismically deficient reinforced concrete buildings.

Investigation of low‐disturbance seismic retrofit method for steel column bases using curved members

AbstractSeismic retrofit has always been a very important subject in recent years. However, typical retrofit techniques such as load‐resisting systems, damper devices, and seismic isolation systems will cause considerable disturbances to the structural system, such as increased force demand, and the building's occupants will need to be temporarily relocated during the construction. A design of the low‐disturbance retrofit method for steel column bases that uses the advantages of the curved member has been proposed in the study to improve seismic performance and reduce the mentioned demerits above. The basic mechanism of the curved member retrofit system was first analytically evaluated by preliminary modeling, followed by a parametric study to verify the effective shape. Four curved member specimens were tested with variations in fabrication processes and boundary conditions. Several aspects, including overall behavior, strength backbones, and deformation shapes of the specimens, were examined upon measured responses. The hysteretic performance of the curved member retrofit system is verified to achieve a stable cyclic behavior with limited strength degradation. A set of physical equations for estimating the lateral loads were established and verified by developing numerical models with a good agreement that enabled them to accurately represent the measured responses in the test.

Research on Reinforcement Technology of Existing Frame Structure with Externally Attached U-Shaped Steel Plate Sub-Structure

With the improvement of building technical requirements and the updating of standards, the demand for the reinforcement of existing buildings is increasing. In order to solve the problem regarding the low economic applicability of the traditional seismic retrofit method, this paper proposes a seismic retrofit method for an externally attached U-shaped steel plate sub-structure that follows the concept of “reinforcing while using”, is composed of a U-shaped steel plate and herringbone channel steel, and can meet the needs of multiple retrofits. Based on the results of a pseudo-static test, the mechanical properties of one unreinforced frame and three reinforced frames with different specifications for the U-shaped steel plate sub-structure were comparatively studied, and the effectiveness and rationality of the reinforcement method were analyzed. The results show that the externally attached U-shaped steel plate sub-structure has good deformation and energy dissipation capacity and can effectively improve the horizontal bearing capacity of an existing frame without changing the original failure mode. The bearing capacity of the three reinforced frames was 1.43, 1.89, and 2.57 times that of the unreinforced specimen. The initial lateral stiffness of the frame also increased significantly, namely, to 1.41, 2.02, and 2.08 times that of the unreinforced specimen, and the stiffness degradation rate decreased. The seismic performance of the original frame was greatly improved.

Seismic capacity evaluation of existing reinforced concrete buildings strengthened with a novel prestressing steel frame system for increasing lateral strength

In this study, a new concept of seismic retrofit, the Prestressing Steel Frame (PSF) system, is proposed to improve and compensate for the weaknesses of the existing strength-enhancing seismic retrofit method. The PSF system, a construction method that maximizes the advantages of the H-shaped steel frame, innovatively improves the constructability and integrity of existing reinforced concrete (R/C) frames and reinforcement joints. This method is a type of typical strength-increasing reinforcement method that facilitates calculation of the required seismic reinforcement amount, and easily enhances the horizontal strength of shear collapse-type R/C buildings with non-seismic detailing. To review the seismic performance of the proposed PSF method, pseudo-dynamic tests were conducted on a real two-story frame based on an existing R/C building without seismic detailing, and seismic performance was evaluated in terms of load and displacement characteristics, seismic damage level, strength enhancement effect, and displacement control. In addition, based on the results of pseudo-dynamic testing, a hysteresis model was proposed to perform non-linear dynamic analysis of the seismically reinforced structure (two-story frame) with the PSF method. Non-linear dynamic analysis was performed based on the proposed hysteresis model, and the results were compared against that of pseudo-dynamic testing. For the commercialization of the method, non-linear dynamic analysis was conducted on the entire R/C building reinforced with PSF, and the effectiveness of seismic reinforcement was verified by comparing the seismic response load and displacement response before and after reinforcement. In the event of an earthquake with a maximum ground acceleration of 200 cm/s2, which is 2/3 of major earthquakes with a 2400-year recurrence interval stipulated in Korea Design Standard (KDS) 41, shear failure is expected for R/C buildings with non-seismic detailing, while small-scale damage is predicted for buildings reinforced with the PSF method. This shows that the PSF strengthening method is effective in minimizing earthquake damage.

Yüksek Dayanımlı Hafif Beton Paneller Kullanılarak Dolgulu Betonarme Çerçevelerin Güçlendirilmesi

This study proposed a practical seismic retrofit method for RC frames. For this purpose, a quasi-static loading was applied to 8 RC frames in finite element analysis software, Abaqus, and frames were pushed 45 mm laterally. High-strength fiber-reinforced lightweight concrete panels strengthened infill walls inside the RC frames. To apply them to the walls, epoxy binder and polyurethane binder were used, and their behavior was compared. Using panels increased the lateral load capacity of the whole frame according to the numerical analysis performed with Abaqus. In the worst case, the retrofitted frame carried approximately two times the traditionally infilled frame's capacity. In the best case, the RC frame carried 4.29 times the lateral load traditionally infilled frame. Polyurethane binder prevented the separation of panels from walls and provided a ductile behavior to frames even in large drifts.

Seismic Retrofit of Diagonal Tension Members in Steel Deck-Truss Bridges Using CFRP Sheets

This study entailed axial cyclic loading tests conducted on full-scale diagonal tension members of steel deck-truss bridges to evaluate the effects of seismic retrofitting methods using carbon fiber–reinforced polymer (CFRP) sheets. The loading tests were performed on CFRP-retrofitted specimens with varying anchoring lengths of the CFRP sheets. The results indicated that the proposed retrofitting methods, which employed the intermediate-modulus CFRP type (390–450 GPa) and polyurea putty (a ductile adhesive), delayed the plastic buckling of the flanges and substantially increased the load-carrying capacities, stiffnesses, and ductility capacities of the retrofitted diagonal tension members. Additionally, the polyurea putty effectively suppressed the peeling failure of the CFRP sheets. It maintained the cross-sectional integrity between the steel members and CFRP sheets even after the plastic buckling of the flanges and rupture failure of the CFRP sheets. Further, finite-element analyses accurately reproduced the loading test results by considering the nonlinear bond-slip performance of polyurea putty, anisotropic characteristics of the CFRP sheets, and cyclic plasticity properties of steel.

Seismic responses, damage mechanisms and retrofitting methods for deep braced excavation: Centrifuge test and numerical analysis

The current study investigates the nonlinear seismic responses and damage mechanisms of the deep braced excavation, which has rarely been inspected in previous studies. An effective numerical model is developed based on dynamic centrifuge tests to properly capture the responses and damage of the structure under earthquakes. The model is established by using the nonlinear properties of the material (for both soil and structure) and contact. The procedure of constructing the numerical model including determining the material parameters, boundary conditions, and contact properties is elaborated. The seismic responses of the deep braced excavation during earthquakes with increasing levels of earthquake intensity are clearly investigated and compared with those in the static condition. Then, the damage mechanisms of the structure are stated. Finally, different seismic retrofitting methods are proposed; and, the most effective method is suggested. The findings from this study can provide a clear understanding of the seismic responses, damage mechanisms, seismic retrofitting methods, and also recommendations for seismic design applications of deep braced excavations.

SHEAR STRENGTH OF THE STRENGTH–DUCTILITY TYPE SEISMIC RETROFITTING TECHNIQUE FOR EXISTING RC COLUMNS USING PRESTRESSING BAR AND STEEL PLATES

This study explores a seismic retrofit method for existing RC columns using a cast-in-site partial thick hybrid wing-wall (THW) technique. The THW technique plays two important roles: (1) to enable easy and cost-effective construction and (2) to considerably increase lateral strength and ductility. The aim of this study is to experimentally determine the shear resistance (truss and arch mechanism) and shear strength of the columns retrofitted using the THW technique. Based on the analytical assessment of the THW technique, design equations of ultimate shear strength and steel plate thickness are proposed.

Application of timber-based techniques for seismic retrofit and architectural restoration of a wooden roof in a stone masonry church

Recent seismic events in Italy highlighted several vulnerabilities in historical buildings belonging to the national architectural heritage. Among others, monumental constructions such as churches appeared to be prone to local (out-of-plane) collapses of masonry walls, often caused by the presence of poor-quality materials and inadequate connections among structural elements. Seismic retrofitting methods are thus necessary, but should also be reversible, not invasive, and aimed to the architectural conservation of the construction, preserving its historical value. In this framework, the potential of timber-based techniques as reversible and effective methods for seismic strengthening and restoration of buildings is promising. This work presents the case study of St. Andrew's Church in Ceto (Brescia, Italy), a stone-masonry monumental building featuring a timber roof from 18th century. Following several inspections commissioned by the curia of Brescia, the church was found in fair structural conditions, with the exception of the wooden roof, having structural elements poorly or not connected among each other and to the masonry. To reduce the evident seismic vulnerability of the church, the roof was retrofitted with plywood panels, allowing for an affordable, rapid, and easily realizable intervention. In this way, the original timber structure could be preserved, creating an adequate load-carrying capacity for static loads, as well as an effective diaphragm against seismic loads. The conducted calculations and numerical analyses showed that the realized intervention greatly improves the seismic behaviour of the building, demonstrating the benefits of wood-based retrofitting and supporting their use for the preservation of architectural heritage.

Experimental and numerical investigation on seismic performance of retrofitted RC columns with web direct/indirect bonding external H-section

This paper presents experimental and numerical investigations of existing reinforced concrete (RC) columns enhanced by two seismic retrofit methods, web indirect bonding and web direct bonding combined with a steel endplate. The former retrofit system is an H-shaped steel member connected to an existing RC column with anchor bolts and an infilled-concrete layer. The latter is quite similar to the web indirect bonding method but incorporates a steel endplate and a stud bolt layer additionally. Three RC columns with/without the retrofitted methods, designated BC, SC-T2, and SC-T4, were built and tested under cyclic loading. The experimental findings showed that the retrofitted RC columns were superior to the non-retrofitted specimen in terms of initial stiffness, peak strength, and energy dissipation capacity. Based on the experimental responses, finite element (FE) models were developed and verified with the experimental results. The results obtained from the simulations were consistent with those from the experiments, indicating the finite element (FE) models can reproduce the seismic responses of bare and retrofitted RC columns with slight simulation variation. Finally, a parametric analysis was carried out to investigate the effect of the material strength and length of the added components on the seismic behavior of the SC-T2 specimen.

Use of timber panels to reduce the seismic vulnerability of concrete frame structures

This paper discusses a seismic retrofit method that is intended for reinforced concrete (RC) frame structures and that sees the replacement of the existing masonry infills with timber structural panels. The intervention is aimed at enhancing the overall behaviour of the buildings without modifying the original concrete structural system. In the presented research over 200 finite-element models comprising bare, masonry-infilled and retrofitted single-storey single-bay frames were subjected to nonlinear static analyses. The response of the timber-infilled frames was then optimised, thus enabling the definition of a few simple design rules to guide the implementation of the retrofit system. Subsequently, the efficacy of the proposed solution was further investigated by applying the timber-based retrofit to an entire case-study building modelled via finite elements and subjected to nonlinear static pushover analysis. The comparison of the results obtained for the building in the original and retrofitted configurations indicates that the proposed system can favour the development of ductile behaviours and improve the seismic response of RC frame structures significantly.

Seismic Strengthening Effects of Full-Size Reinforced Concrete Frame Retrofitted with Novel Concrete-Filled Tube Modular Frame by Pseudo-Dynamic Testing

The present study proposes a new seismic retrofitting method using a concrete-filled tube modular frame (CFT-MF) system, a novel technique to overcome and improve the limitations of existing seismic strengthening methods. This CFT-MF seismic retrofitting method makes the most of the advantages of both concrete and steel pipes, thereby significantly improving constructability and increasing integration between the existing structure and the reinforcement joints. This method falls into the category of typical seismic retrofitting methods that focus on increasing strength, in which the required amount of seismic reinforcement can be easily estimated. Therefore, the method provides an easy solution to improving the strength of existing reinforced concrete (RC) structures with non-seismic details that are prone to shear failure. In the present study, a full-size two-story test frame modeled from existing domestic RC structures with non-seismic details was subjected to pseudo-dynamic testing. As a result, the effect of the CFT-MF system, when applied to existing RC structures, was examined and verified, especially as to its seismic retrofitting performance, i.e., restoring force characteristics, stiffness reinforcement, and seismic response control. In addition, based on the pseudo-dynamic testing results, a restoring force characteristics model was proposed to implement non-linear dynamic analysis of a structure retrofitted with the CFT-MF system (i.e., the test frame). Finally, based on the proposed restoring force characteristics, non-linear dynamic analysis was conducted, and the results were compared with those obtained by the pseudo-dynamic tests. The results showed that the RC frame (building) with no retrofitting measures applied underwent shear failure at a seismic intensity of 200 cm/s2, the threshold applied in seismic design in Korea. In contrast, in the frame (building) retrofitted with the CFT-MF system, only minor earthquake damage was observed, and even when the maximum seismic intensity (300 cm/s2) that may occur in Korean was applied, small-scale damage was observed. These results confirmed the validity of the seismic retrofitting method based on the CFT-MF system developed in the present study. The non-linear dynamic analysis and the pseudo-dynamic test showed similar results, with an average deviation of 10% or less in seismic response load and displacement.

Pilot Demonstration of a Strengthening Method for Steel-Bolted Connections Using Pre-Formable Carbon Fiber Cloth with VaRTM

In recent years, many seismic retrofitting methods have been performed to improve the structural performance and prevent the brittle failure of structural members. In the case of steel structures, slender seismic braces have been widely used for buildings, towers, and bridges. The brace connections should resist the full plastic axial tension load to ensure adequate plastic deformation performance for vibration energy absorption. However, certain connections do not satisfy these requirements. Recently, carbon fiber reinforced plastic (CFRP) has been used extensively to strengthen existing structures because of its high-strength, high elastic modulus, and light-weight characteristics. In this paper, we investigate the applicability of CFRP strengthening for brace connections and gusset plates with stepped surfaces using the vacuum-assisted resin transfer molding technique as a pilot demonstration. Stepped surfaces can be eliminated by using alternative CFRP layers to straighten the structural CFRP layers in order to effectively transfer the axial stress. Eventually, it is shown that CFRP strengthening can improve the connection strength and plastic deformation with 3% elongation, even if the CFRP is molded on the stepped surface.

철골 내진보강공법 길이조절형 간접접합부의 전단내력평가를 위한 실험적 연구

철골 내진보강공법 길이조절형 간접접합부의 전단내력평가를 위한 실험적 연구

NHERI@UC San Diego 6-DOF Large High-Performance Outdoor Shake Table Facility

Since its commissioning in 2004, the UC San Diego Large High-Performance Outdoor Shake Table (LHPOST) has enabled the seismic testing of large structural, geostructural and soil-foundation-structural systems, with its ability to accurately reproduce far- and near-field ground motions. Thirty-four (34) landmark projects were conducted on the LHPOST as a national shared-use equipment facility part of the National Science Foundation (NSF) Network for Earthquake Engineering Simulation (NEES) and currently Natural Hazards Engineering Research Infrastructure (NHERI) programs, and an ISO/IEC Standard 17025:2005 accredited facility. The tallest structures ever tested on a shake table were conducted on the LHPOST, free from height restrictions. Experiments using the LHPOST generate essential knowledge that has greatly advanced seismic design practice and response predictive capabilities for structural, geostructural, and non-structural systems, leading to improved earthquake safety in the community overall. Indeed, the ability to test full-size structures has made it possible to physically validate the seismic performance of various systems that previously could only be studied at reduced scale or with computer models. However, the LHPOST's limitation of 1-DOF (uni-directional) input motion prevented the investigation of important aspects of the seismic response of 3-D structural systems. The LHPOST was originally conceived as a six degrees-of-freedom (6-DOF) shake table but built as a single degree-of-freedom (1-DOF) system due to budget limitations. The LHPOST is currently being upgraded to 6-DOF capabilities. The 6-DOF upgraded LHPOST (LHPOST6) will create a unique, large-scale, high-performance, experimental research facility that will enable research for the advancement of the science, technology, and practice in earthquake engineering. Testing of infrastructure at large scale under realistic multi-DOF seismic excitation is essential to fully understand the seismic response behavior of civil infrastructure systems. The upgraded 6-DOF capabilities will enable the development, calibration, and validation of predictive high-fidelity mathematical/computational models, and verifying effective methods for earthquake disaster mitigation and prevention. Research conducted using the LHPOST6 will improve design codes and construction standards and develop accurate decision-making tools necessary to build and maintain sustainable and disaster-resilient communities. Moreover, it will support the advancement of new and innovative materials, manufacturing methods, detailing, earthquake protective systems, seismic retrofit methods, and construction methods. This paper will provide a brief overview of the 1-DOF LHPOST and the impact of some past landmark projects. It will also describe the upgrade to 6-DOF and the new seismic research and testing that the LHPOST6 facility will enable.

Development and seismic retrofit of an innovative modular steel structure connection using symmetrical self-centering haunch braces

As an efficient and environment-friendly technique that combines off-site manufacturing of modules and on-site assembly, modular buildings have been adopted in many areas of the construction industry. This paper proposes an innovative modular steel structure (MSS) connection with bolted cover plates, which inserts a cross-shaped plug-in connector inside the adjacent columns to achieve accurate positioning in the module installation and provide partial shear capacity. A seismic retrofit method using hinged diagonal self-centering (SC) haunch braces is proposed for the MSS connection to improve the seismic performance and achieve functional recoverability after earthquakes. Hysteretic behaviors of the MSS connection and the self-centering MSS (SC-MSS) connection are investigated due to cyclic loadings. Results demonstrate that compared with the MSS connection, the SC-MSS connection is expected to improves strength and stiffness and exhibits stable flag-shaped hysteretic responses with a satisfactory self-centering capability. The hinged diagonal SC haunch braces are capable of reducing the average stress level around the connection core region, controlling the development of plastic damage, avoiding the local failure, and improving the ductility of connection. The present study provides practical connections and important guidance for the applications of modular steel structures in the medium- and high-intensity seismic regions.

Experimental Study on Seismic Retrofitting of Reinforced Concrete Frames Using Welded Concrete-Filled Steel Tubes

Buildings constructed with non-seismic details are at risk of damage and collapse when an earthquake occurs due to a lack of strength, stiffness, and ductility. For reinforced concrete (RC) moment-resisting frames, seismic retrofitting methods that can enhance strength or ductility should be applied. However, such strategies have many disadvantages related to constructability, serviceability, securing integrity, and cost. In this paper, a welded concrete-filled steel tube (WCFST) system was examined in order to resolve the problems of the existing seismic retrofitting methods for RC moment-resisting frames. To evaluate the seismic performance of the proposed system, two specimens, one with non-seismic details and another reinforced with a WCFST seismic system, were manufactured for the cyclic loading tests. As a result of the experiments, the specimen retrofitted with the WCFST system showed maximum load, effective stiffness, and energy dissipation capacity values approximately 3, 2, and 2.5 times greater, respectively, than those obtained from the existing reinforced concrete frame specimen. The experimental results indicate that the proposed WCFST system is expected to be effective at improving the seismic performance by enhancing both the strength of the existing reinforced concrete frame structures and the dissipation of the seismic energy.

The Pushout Test of Seismic Reinforcement System (SRM) Connection that Respond to Earthquake Extensive Level

This paper introduces a state-of-the art seismic retrofit method (SRM) that has the resistance mechanism of eccentrically braced frames (EBF). In EBF, local failure is induced to the link beam such that other members remain in the elastic state when an earthquake load is applied. SRM works by attaching to an existing building in the form of an external frame to enhance its seismic performance. The seismic reinforcement of medium- and low-rise reinforced concrete buildings has a small inter-story drift; hence, the adhesion between the two materials has a great influence on the seismic reinforcement effect. In this study, a push-out test was performed to show the adhesion performance under various conditions. The performance of various attachment methods was also explored to improve adhesion with the RC structure for securing the performance of the SRM system. Additionally, this study proposes a shear strength equation that considers the influence of the contact direction of steel, increase in plate thickness, and anchor yield strength. The test results indicated that it can be used as a new shear strength equation as the error rate is within 10% compared to the experimental results. Although the web direct bonding method using end plates is disadvantageous in terms of processability, it showed the highest strength improvement results. Furthermore, the chemical anchor (Hilti) connection exhibited stable performance results regardless of the bonding method.